1. Field of the Invention
This invention relates generally to the field of oil and gas well stimulation, and more particularly, to isolating segments of a subterranean cased or open hole well for stimulating and/or testing purposes. The invention is particularly well-suited for stimulating horizontal wellbores that extend through a naturally fractured reservoir.
2. Description of the Related Art
The field of oil and gas well stimulation sometimes involves wells with multiple horizontal laterals in a vertical well that are drilled to facilitate production from a formation. Some of the well laterals are substantially long, up to several thousand feet, and it is desirable to stimulate these horizontal well sections to increase their production. There are a number of stimulation methods, such as acidizing and fracturing. The typical way to stimulate the horizontal sections of a wellbore is to fill the entire horizontal wellbore with the desired stimulation fluid, increase the fluid pressure, and hope that the fluid encounters and enhances the formation's natural fractures. However, according to recent studies this method of stimulating a long horizontal section of a well only effectively treats the initial interval (e.g. the first one-thousand feet or so) of that section. It is desirable to enhance the natural fractures in the formation all the way to the end of the horizontal well, but current methods do not effectively provide for this. In order to effectively fracture a long horizontal well, the well needs to be isolated into sections which can each be independently stimulated.
One way to isolate horizontal sections of a well in anticipation of fracturing is to use inflatable packers. Inflatable packers can be maneuvered into a desired section of the horizontal well and set to isolate the section. However, inflatable packers have a limited pressure containing capacity, often not enough to facilitate fracture of a formation, and therefore they have a high tendency to fail and add significant downtime to the completion operation.
There is another tool, the Wizard Packer from Dresser, that allows isolation of a horizontal well into preset lengths to facilitate stimulation of the formation, but it requires sending darts into the sections to open sliding sleeves which allow the treating fluid to enter into the isolated section. Despite the isolation, there is sometimes still no stimulation within the preset segment if one or more of the interval sections does not contain a natural fracture to enhance. There is no way to adjust the isolated length and effectively stimulate a new length without removing and resetting the entire system. The Wizard Packer is often prohibitively expensive, and is not retrievable. The Wizard Packer is fairly long in length and rigid, such that it often cannot negotiate small radius turns in a wellbore. There is a need for a less expensive, more maneuverable tool to isolate sections of the horizontal lateral at any length without removing the tool from the wellbore since the time and expense for each entry and withdrawal of a tool from a well is significant. The location of the natural fractures within a wellbore may not be known, and presetting the isolated lengths allows no flexibility for moving and adjusting the sections to find natural fractures to enhance.
In addition, there is no effective method of testing the sections of a horizontal wellbore for their respective production levels following stimulation.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.